For some reason, adding reflex sights to my weapon with a scope does not reduce its aim level. When used individually, they work correctly. The 7x scope gives -2 aim levels and the reflex sight gives +1. But when added together why does the reflex sight nor reduce the combined aim levels to +1? Are they supposed to be mutually exclusive? I'm using the latest build with NCTH.

Since you can look through only one scope at a time effectively, the modifiers do not stack. You can cycle through the various sighting options with the [.] (dot) key however to adapt to varying combat ranges.

Other way to reduce the aim levels :
- traits like gunfighter/sniper
- one weapon has a scope+reflex sight combo (don't remember which one but it's an assault rifle. Also maybe an attachment scope+reflex sight exist but i'm not sure right now).

Wouldn't it make more sense for the Auto Weapons and Machinegunner traits to reduce aim levels, too? Maybe those reduce the aim levels for Assault Rifles and LMGs, while Sharpshooter and Sniper reduce it for Sniper Rifles and Rifles.